The danger of personal injury in motor vehicle accidents can be substantially mitigated by the use of passive restraint systems, such as an airbag system, or other safety systems. These systems frequently include an inflatable balloon, called an airbag, which normally is stored away in a location such as a compartment within the vehicle steering wheel or within a side pillar. When the vehicle suffers an impact from a stationary object or another vehicle, the attendant rapid deceleration of the vehicle can be measured with sensors such as microelectromechanical (“MEMS”) accelerometers. When the sensors indicate that deceleration thresholds have been exceeded, deployment of the airbag(s) is triggered. Airbag inflation at the proper time can often prevent substantial injury to passengers by restraining passenger movement in a crash. (As used herein, the term “passenger” will include a vehicle driver.)
Prevention of a false deployment of a passive restraint is as important as deploying the restraint at the proper time. An inflated airbag, for example, can interfere with a driver's ability to control the vehicle, thereby causing a crash. As a result, prior art passive restraint systems have frequently incorporated additional sensors called “safing” sensors. Restraints are activated only when both the safing sensor and the acceleration sensor indicate the need for passenger restraint. However, such redundancy is an undesirable additional expense. U.S. Pat. No. 6,487,482 discloses a system with two sensors that implement “reciprocal” plausibility checks.